1. Field of the Invention
The invention relates to a simple resettable fuse device that can be used in digital and analog integrated circuits for the adding or removing circuit elements on a dynamic basis.
2. Background Information
Fuse devices are useful in integrated circuits for disconnecting or disabling failed circuit elements. In a RAM cell array, for example, it is well known in the art to fabricate on the silicon chip miniature metallic fuses that are in series with the memory data lines. If in the process of testing during the manufacturing cycle, a defective memory location is detected, the appropriate hard fuse can be severed, rendering the bad location inoperable. While simple to fabricate, a disadvantage of the hard fuse is that the change is permanent. Moreover, once the RAM cell array is sealed after testing, any further failures of memory locations cannot be cannot corrected by severing fuse links, and the entire device may have to be scrapped.
Another disadvantage of hard fuses is they are severed by laser cutting and therefore must be placed away from other sensitive parts of the chip. This tends to increase the distance that signals on the data lines must travel, an undesirable feature in high speed, high density, microelectronic circuits.
Soft fuse devices disclosed in the prior art overcome some of the disadvantages of using hard fuses in integrated circuits. For example, U.S. Pat. No. 6,384,665 to Smoszna discloses the use of a programmable soft fuse for disabling a signal line in a RAM cell array, which includes an electronic switching circuit, a latch, a control circuit and a reset circuit. In Smoszna, these circuits are used in conjunction with an address decoder to test the RAM cell array to locate failing bits, word lines or bit lines on the array, and enter the location of the bad bits into the decoder. When the address does not correspond to a failed bit, the latches of the corresponding programmable soft fuse are set so as to allow the address signal to go to the array. However, if the address corresponds to one of the failed bits, then the latches are set so as to prevent the address signal form going to the array, and in that case, additional shifting circuitry connected to the address decoder can reroute the data to another redundant word line or bit line.
While soft fuses disclosed in the prior art address some of the shortcomings of hard fuses, what is needed is simple soft fuse device that can be adapted to use in a variety of digital and analog integrated circuits.